1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to tamper-resistant electrical wiring devices.
2. Technical Background
Electrical power is provided to users by way of electrical distribution systems that typically include electrical wiring from a utility power source to a breaker panel disposed in a house, building or some other facility. The breaker panel distributes AC power to one or more branch electric circuits installed in the structure. The electric circuits may typically include one or more electrical wiring devices that regulate, monitor or provide AC power to other devices. Each electrical wiring device is equipped with electrical terminals that provide a means for connecting the device to the source of AC power and a means for connecting the device to a load. Specifically, line terminals couple the device to the source of AC electrical power, whereas load terminals couple power to the load. Load terminals may also be referred to as “feed-through” or “downstream” terminals because the wires connected to these terminals may be coupled to a daisy-chained configuration of receptacles or switches.
Thus, an electric circuit may include many different electrical wiring devices disposed at various locations throughout a structure. Outlet receptacles, switches and protective devices are examples or types of electrical wiring devices. Ground fault circuit interrupters (GFCIs), and are fault circuit interrupters (AFCIs) are examples of protective devices in electric circuits. Switches, protective devices and other types of electrical devices are often provided in combination with receptacles. For example, outlet receptacles are disposed in duplex receptacles, raceways, multiple outlet strips, power taps, extension cords, light fixtures, appliances, and the like. When the wiring terminations of these devices (i.e., wiring terminals, plugs, etc.) of these devices are connected to the electrical distribution system, the receptacle contacts may be energized. When the power cord of an electrical appliance is inserted into the receptacle outlet, the electrical appliance is also energized or capable of being energized (i.e., turned ON).
The insertion of a foreign object into an outlet receptacle opening is usually a safety hazard. For example, young children and toddlers are known to have a proclivity toward inserting objects such as paper clips or screwdriver blades into receptacle contact openings. (This should be a cause for alarm, especially in light of the fact that, e.g., GFCIs are configured to trip in response to a mere 6 mA current). Even a small current (in the mA range) passing through a human body to ground can result in an electric shock, burns, or electrocution (a fatal shock event). As a result, the use of shutters has long been a means for preventing foreign objects from making contact with the receptacle contacts disposed within the receptacle openings. One drawback to this approach relates to the ineffectiveness of related art designs. In many conventional designs, the shutters will typically open when objects are placed into both openings and expose the person to a shock hazard. What is needed is a shutter mechanism that only opens when an actual corded plug is inserted into the receptacle.
Another drawback to this approach relates to the complexity of related art shutters. Many shutter designs comprise multiple parts and spring elements. For example, in one conventional approach that has been considered, the shutter must be intricately installed within a base platform (by hand) after positioning a delicate leaf spring element within the base. The cost and time of assembling the shutter mechanism, and the space taken up by their multiple parts, limit the usage of these designs. Moreover, automated environments often generate vibrations and mechanical forces that tend to introduce failure modes. Specifically, vibrations tend to cause the leaf spring to become dislodged or otherwise become separated from the platform. In addition, when objects are inserted into the receptacle opening, the shutter is forced to press against the leaf spring while moving upwardly and downwardly within the base platform. This type of movement increases the likelihood that the leaf spring will be dislodged. Once this happens, the receptacle device is either inoperable or unprotected.
Another drawback to conventional shutter designs relates to the assumption that keyed receptacle openings will ensure that the plug blades are inserted into the receptacle openings simultaneously. While this is true to a certain extent, there is still a great deal of room for skewing and side-to-side movement until the blades are captured by the receptacle contacts. For example, in real life, when someone attempts to insert a corded plug into a receptacle opening, they very often wiggle the plug in an effort to align the plug blades with the cover apertures. These back and forth skewing movements cause the plug blades to strike the shutter with varying amounts of force at different instants of time (not simultaneously). Similar issues can be caused by plug blades that are bent or not of the same length. Conventional shutters typically employ a linear slide motion and become jammed and inoperative after they absorb repeated nicks and gouges.
What is needed is a shutter assembly that is configured to operate smoothly (and robustly) even when foreign objects or uneven plug blades are forcefully inserted. What is also needed is a relatively simple protective shutter assembly that is easy to install within an electrical wiring device. What is needed is a shutter assembly that can freely float to prevent the aforementioned jamming issues.